Just go to Wal Fart and spend $19.88 on a 12gal Igloo w/o a drain, or $24.88 w/ a drain.
$25 for 2 inch thick insulated styrofoam sheet that's 4ft x 8ft (will make 8 lids), from Lowes.
$5 for Aluminum Foil Tape to COMPLETELY wrap the lid.
Use THE BOTTOM of your net pots as a stencil since the top of the pots plus the rim, is wider than the bottom.
Take a simple steak knife and cut out the hole.
Wrap the inside of the cut outs with tape too, or the styrofoam will get wet and soaked from the inside-out.
Run your tubing over the edge of the cooler and under the lids, like me.
OR, use a #2 pencil to poke holes at a 45 degree angle (blocks light) instead of straight down, and run the tubing that way.
Bottom line is you're going to battle high water temps unless you have a chiller running constantly, bcuz even frozen water bottles won't be enough after a while.
Just the facts of it.